Diet plans are no holy books, but being in control is extremely sexy. IF you follow some regimen, then you definitely have a goal, and whatever goal that may be ( losing weight, building muscles..etc.), it is completely dedicated to bettering your health.
If you are on a strict diet, like a ketogenic one, sorry.. the answer is not to cheat.
Most diets however recommend cheating, for the psychological satisfaction that the indulgence of high calories create. Cheat a meal, not a day. Use the 90/10 rule, where 90% of the time you stick to your healthy eating plan, and the other 10%, you feed your fondness of chocolate chip cookies and saucy burgers.
Many dietitians have lit the green light on this. Cheating time will be a motivation to carry on through pizza-less days. The answer is: to cheat ( and do it passionately).